In the refining of petroleum to yield usable products, an essential processing step is hydrotreating. The major purposes of hydrotreating include the conversion of organosulfur and organonitrogen compounds to H.sub.2 S and NH.sub.3, respectively, the removal of metals contained in the petroleum fraction, and the hydrogenation of olefins and occasionally aromatics. This step is carried out by reacting a petroleum fraction with hydrogen in the presence of a catalyst consisting of a group VIb metal such as Mo, sometimes promoted with group VIII metals, especially Co and/or Ni, on an inert support.
Hydrotreating catalysts are supplied as the metal oxides and ar presulfided to convert the metal oxides to their sulfides. Presulfiding is likewise required after air-regeneration of a hydrotreating catalyst (to remove coke), since this results in a reconversion of the metal sulfides to metal oxides. By presulfiding under carefully controlled conditions prior to hydrotreating, coke formation, which leads to catalyst deactivation, is minimized. Presulfiding is typically carried out by passing a mixture of hydrogen gas and either H.sub.2 S or a labile organosulfur compound over the catalyst. Alternatively, it can be done by passing H.sub.2 S or CS.sub.2, in the absence of hydrogen gas, over the catalyst, followed by treatment with hydrogen gas. Appropriate labile organosulfur compounds include CS.sub.2, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), di-t-nonyl polysulfide (TNPS), or a lower-alkyl mercaptan such as ethyl mercaptan or butyl mercaptan. Such art has been described in U.S. Pat. Nos. 3,016,347, 3,132,086, and 3,140,994.
The methods currently practiced have been described by Hallie (Oil and Gas Journal, Dec. 20, 1982, pp. 69-74) and include vapor-phase and "spiked" liquid feed presulfiding. A "spiked" liquid feed consists of a paraffinic base such as kerosene to which the sulfiding agent has been added to give a solution typically containing 1-3 wt. % S. Each of these methods involves bringing the presulfiding agent(s) or feeds and hydrogen gas simultaneously into contact with the catalyst at elevated temperatures after it has been loaded into the hydrotreating reactor. Hallie teaches that spiked-feed presulfiding results in higher catalyst activity than vapor-phase presulfiding, but that the activity of the sulfided catalyst is independent of the choice of spiking agents listed in the above paragraph.
The present invention relates to an organosulfide-impregnated catalyst that can be made prior to its insertion in a hydrotreating reactor.